Arteriole
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[[Image:Illu capillary.jpg|thumb|300px]]
An '''arteriole''' is a small diameter [[blood vessel]] that extends and branches out from an [[artery]] and leads to [[capillary|capillaries]]. <ref>{{cite book
| last = Maton
| first = Anthea
| authorlink =
| coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright
| title = Human Biology and Health
| publisher = Prentice Hall
| date = 1993
| location = Englewood Cliffs, New Jersey
| pages =
| url =
| doi =
| id =
| isbn = 0-13-981176-1}}</ref>
Arterioles have thin [[muscle|muscular]] walls (usually only one to two layers of smooth muscle) and are the primary site of ''vascular resistance''<ref>[http://www3.umdnj.edu/histsweb/lab7/lab7arterioles.html arterioles<!-- Bot generated title -->]</ref>.
[[Blood pressure]] in the arteries supplying the body is a result of the work needed to pump the [[cardiac output]] (the flow of blood pumped by the heart) through the ''vascular resistance'', usually termed [[total peripheral resistance]] by physicians and researchers.
==Natural fluctuation==
The up and down fluctuation of the [[arterial]] blood pressure is due to the pulsatile nature of the [[cardiac output]] and determined by the interaction of the [[stroke volume]] versus the volume and elasticity of the major arteries.
In a healthy vascular system the [[endothelium]], inner lining of arterioles and other blood vessels, is smooth and the vessel is relaxed.
This healthy condition is promoted by the ample production of [[nitric oxide]] in the endothelium, which biochemical reaction is regulated by a complex balance of [[polyphenol]]s, various [[nitric oxide synthase]] [[enzyme]]s and L-[[arginine]]. In addition there is direct communication via gap junctions between the endothelial cells and the vascular smooth muscle
==Pathology==
Any pathogen which constricts blood flow, such as [[stenosis]], will increase total peripheral resistance and lead to [[hypertension]].
==Medication==
The muscular contraction of arterioles is targeted by drugs that lower blood pressure ([[antihypertensive]]s), for example the [[dihydropyridine]]s ([[nifedipine]] and [[nicardipine]]), which block the [[calcium channel blocker|calcium conductance]] in the muscular layer of the arterioles, causing relaxation.
This decreases the resistance to flow into peripheral vascular beds, lowering overall systemic pressure.
==Metarterioles==
A "[[metarteriole]]" is an arteriole which bypasses capillary circulation.<ref>{{GeorgiaPhysiology|3/3ch9/s3ch9_2}}</ref>
==References==
{{reflist}}
{{cardiovascular_system}}
[[Category:Cardiovascular system]]
{{circulatory-stub}}
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